1. Field of the Invention
This invention relates to a windshield for a head-up display system and in particular to an automotive windshield functioning as the combiner for the head-up display system and having a wedged configuration for some selected portion of the windshield area, particularly in the viewing area of the head-up display, to eliminate double imaging and the interlayer used to provide the required wedged configuration.
2A. Technical Considerations
A head-up display system is a visual display arrangement that displays information to a viewer while he simultaneously views the road and objects outside his vehicle around and through the display. Head-up display systems are often incorporated into aircraft cockpits for pilots to monitor flight information. More recently the systems have been used in land vehicles such as cars, trucks and the like. The display is generally positioned so that the viewer does not have to glance downward to the vehicle dashboard and away from the viewing area in front of the vehicle as is required of a vehicle operator viewing vehicle operating information in a vehicle not having a head-up display.
A head-up display system generally includes a display projection system, a collimator, and a combiner. The projection system includes a light source that projects operating information through the collimator which generally aligns the projected light rays. The collimated light is then reflected off the combiner, which is in the vehicle operator""s field of view. In this manner, vehicle information such as, for example, fuel information and vehicle speed is displayed within the operator""s field of vision through the windshield and permits the operator to safely maintain eye contact with the road and other objects outside his vehicle while simultaneously viewing the displayed information. The reflected images of the display may be focused at a position anywhere from immediately in front of the vehicle to optical infinity.
Laminated windshields have been used as the combiner in a head-up display system to reflect a primary display image as taught in U.S. Pat. No. 2,264,044 to Lee. However, it has been observed that a secondary image is reflected off the outer surface of the windshield. This secondary image is superimposed over but offset from the primary image and reduces the overall image clarity.
It would be advantageous to have a windshield for a head-up display system which functions as a combiner and provides a clear display image without producing double images when viewing through the head-up display area, without distorting the view through other portions of the window not associated with the head-up display system, and without incorporating additional components with the windshield.
2B. Patents of Interest
U.S. Pat. No. 1,871,877 to Buckman teaches a display system having a glass sheet mounted on the windshield or dashboard which reflects instrumentation information to the vehicle operator.
U.S. Pat. No. 2,264,044 to Lee teaches a motor vehicle having an illuminated speedometer display that is reflected off the inboard surface of the vehicle windshield.
U.S. Pat. No. 2,641,152 to Mihalakis teaches a vehicle projection device wherein instrumentation information is reflected off of a reflecting screen on the inboard surface of the vehicle windshield. The reflecting surface has a satin finish and can be metal, glass, or plastic.
U.S. Pat. No. 2,750,833 to Gross teaches an optical display system for eliminating double images which occur in reflector type sights such as those used in aircraft gun sighting installations. A collimated light beam is polarized and separated into two ray branches. One of the two ray branches is then eliminated.
U.S. Pat. No. 3,276,813 to Shaw, Jr. teaches a motor vehicle display system which utilizes a highly reflective coating on the inboard surface of the vehicle windshield to reflect instrumentation information to the vehicle operator.
U.S. Pat. No. 3,446,916 to Abel teaches an image combiner utilizing a portion of the aircraft window. The inner surface portion of the window is coated with a partially reflective film.
U.S. Pat. Nos. 3,554,722, 3,591,261, and 3,647,285 to Harvey et al. teaches a double glazed glass window structure which eliminates objectionable fringe patterns produced in this structure when float glass of non-uniform thickness is utilized. The window structure includes a pair of spaced apart, float glass sheets one or both of which are tapered from a thick edge to an opposing thin edge. When both the glass sheets are tapered, the glass sheets are positioned such that a thick edge of one glass sheet is spaced from a thin edge of the opposing glass sheet.
U.S. Pat. No. 3,697,154 to Johnson teaches an optical viewing system in which images formed on the screen of a cathode ray tube (CRT) are reflected from a curved mirror having a general aspheric surface of revolution to a partially reflective combiner having two nonparallel hyperboloid surfaces, the combiner being positioned in the normal line of sight of an observer such that a collimated CRT image is reflected from the near surface of the combiner to the observer""s eyes and the combiner being adapted to transmit light incident from the outside so that the CRT display is superimposed without parallax on the real world to provide a head-up display.
U.S. Pat. No. 3,870,405 to Hedges teaches a visor for use an optical element in a helmet-mounted sight having inner and outer surfaces being sections of focal paraboloids of revolution.
U.S. Pat. No. 3,899,241 to Malobicky, Jr. et al. teaches a windshield adapted for use in aircraft and includes a transparent reflective coating on the inboard surface in the center portion of the forward vision area to form a vision image receiving area. Vehicle information is reflected off the reflective coating to the vehicle operator.
U.S. Pat. No. 3,940,204 to Withrington and U.S. Pat. No. 4,218,111 to Withrington et al. teach an optical display system utilizing holographic lenses.
U.S. Pat. No. 4,261,635 to Freeman teaches a head-up display system including a holographic combiner positioned inboard of the vehicle windshield. The hologram is disposed substantially orthogonal to and midway along an axis between the observer""s eye position and the projection optics so as to deviate light from an image produced by the projection optics to the observer eye with minimal field aberration.
U.S. Pat. No. 4,398,799 to Swift teaches a head-up display system which simultaneously records the pilot""s view by reflecting the outside scene and the projected display by reflecting the outside scene and superimposed display off a mirror mounted on the pilot""s helmet and recording the reflected view with a camera mounted on the pilot""s helmet.
U.S. Pat. No. 4,613,200 to Hartman teaches a head-up display system which uses two parallel holographic optical elements to reflect instrumentation information to the vehicle operator. One of the elements is made part of or attached to the vehicle windshield.
U.S. Pat. No. 4,711,544 to Iino et al. teaches a display system for a vehicle wherein instrumentation information is reflected off the front glass of the vehicle so that the image display can be formed in a desired position, aligned with the line of sight of the driver without obstructing the front sight of the driver.
U.S. Pat. Nos. 4,787,711 and 4,892,386 and European Patent No. 229,876 to Suzuki et al. teach an on-vehicle head-up display device employing a catoptric system for a windshield glass of an automobile to project a display image onto an inner surface of the windshield glass, an optical system for letting a virtual image of the display image of the display means enter the windshield glass is adapted to make an angle formed by light beams of the virtual image entering the windshield glass less than a monocular resolving power and an optical means for correcting parallax of the light beams of the virtual image is provided between the optical system and the windshield glass to thus eliminate double imaging and binocular parallax.
Defensive Publication No. T861,037 to Christensen teaches a tapered or wedged vinyl interlayer for use in laminating windshields such that the interlayer is thicker at the top of the windshield than at the bottom of the windshield in order to eliminate double vision caused by the windshield curvature and angle of installation.
The present invention provides a windshield for a head-up display system that reduces the degree of double imaging that occurs when a laminated windshield is used as the combiner in the display system. The windshield functions as a combiner for the head-up display system without requiring any additional reflecting or transmitting elements or components to be incorporated onto or into the windshield assembly. The windshield in the present invention is constructed such that selected opposing, outer major surfaces of the windshield are non-parallel with the opposing outer major surfaces oriented relative to each other so that an image, projected from a display source and reflected off a first major surface of the windshield, is substantially superimposed over or parallel to the same image from the display source reflected off the opposing outer major surface of the windshield.
In one embodiment of the invention the windshield has a selected area that has the outer major surfaces of the windshield non-parallel to one another, and the outer major surfaces of the windshield at the remaining area generally parallel to one another. In this manner, the degree of double imaging is reduced in the area where the outer surfaces are non-parallel to one another, and the optical distortion in the remaining area is improved because the outer surfaces are parallel to one another. This may be accomplished by having one or both of the glass plies and/or the sheet of interlayer material partially tapered in thickness such that when the plies and sheet are joined together, the outer major surfaces of the windshield in the selected area are nonparallel to one another with the remaining area of the outer major surfaces of the windshield generally parallel to one another in the area other.
The present invention also provides an interlayer blank for use with a glass ply in a vehicle windshield for a head-up display system. The blank is polyvinylbutyral and includes a first portion with a predetermined thickness profile and a second portion with a tapered thickness profile different from the predetermined profile. The interlayer may be provided by casting the interlayer to the desired configuration, extruding the desired cross sectional thickness, or differentially stretching the interlayer to the desired shape or through a combination of these processes. In one particular embodiment of the invention, interlayer having a desired varying thickness profile is produced by initially forming the interlayer with a thickness profile greater than the desired profile and subsequently differentially stretching the interlayer to reduce the thickness of the interlayer such that its thickness corresponds to the desired thickness profile.
When the glass plies and the interlayer having the tapered section are assembled and laminated to form a unitary structure, the opposing major surfaces of the laminate are non-parallel in the area of the tapered section and offset at a predetermined angle in the vicinity of the tapered section. The windshield in use is positioned relative to a display system such that the images generated by light rays from the display source reflected off the non-parallel opposing major surfaces of the windshield or laminate are substantially superimposed over or parallel to each other such that double imaging is reduced if not eliminated, while the remaining sections of the windshield have the outer major surfaces substantially parallel to one another to eliminate or minimize optical distortion of objects viewed through the remaining area of the windshield.
The invention also contemplates making the windshields of the instant invention by joining glass sheets and a sheet of interlayer material to provide a windshield having the outer surfaces parallel in a first predetermined area and nonparallel in a second predetermined area.